Among fuels derived from plant biomass, ethanol has received particular attention as a potential replacement for or supplement to oil-derived products.
Production of ethanol from biomass is normally obtained through the fermentation process of raw biological material rich in sugar or starch such as grain, sugarcane or corn also referred as first generation bio-ethanol.
To minimize the production cost and increase the potential of bio-ethanol produced from biomass, it is crucial to use lignocellulosic biomass in the form of low-cost byproducts from gardening, agriculture, forestry, timber industry and the like; thus for example, materials such as straw, maize stems, forestry waste, sawdust and wood-chips. Ethanol produced from this type of biomass is also referred to as second generation bio-ethanol.
Lignocellulosic biomass contains sugar polymers in form of hemicelluloses and cellulose. Before those sugars can be fermented to ethanol the sugar polymers has to be broken down to its sugar monomers. A common way to brake down the polymers is to use enzymatic hydrolysis. To increase the availability of the biomass to the enzymes the lignocellulosic biomass often undergoes a thermo/chemical pre-treatment. Following a thermochemical approach such a process often requires that the temperature of the biological matter is raised to a temperature being above the boiling temperature of the liquid in which the biological matter is contained. Therefore, one is often faced with the problem of pressurising a slurry or a pulp containing the biological matter so that the temperature can be increased to temperatures above the boiling temperature of the liquid while maintaining the fluid in a liquid state. When considering this problem within the preparation of biomass for fermentation, the temperature of the slurry or pulp containing the biological matter needs to be around 140-200° C. in order for the preparation process to be carried out and this is the question of producing sufficient activation energy within the material.
Another problem, that is particularly relevant in biomass, is the rate of change of the temperature of the slurry or pulp containing the biological matter. It has been found that the rate of change of the temperature should be as high as possible to reduce the time at elevated temperature to reduce the amount of unwanted chemical side reactions. Optimally, the time at elevated temperature should be reduced to only the time it takes for the desired reactions to take place at the desired temperature.
A particular relevant problem to be solved is to avoid overheating of the slurry or pulp containing the biological matter. Such overheating means that the slurry or pulp is heated to a temperature being above the desired temperature aimed at. Such overheating results in that unwanted side reactions may occur rendering the quality of the prepared slurry or pulp lower. Often the overheating is the result of locally applying heat to the slurry or pulp by e.g. a heating surface that is heated to a temperature above the desired reaction temperature in order to produce heat conduction through the slurry or pulp based on a temperature gradient. In other situation that tends to limit the overheating issue steam is often used to heat slurry or pulp and is introduced as steam into a reactor and the condensation of steam tends to limit heat transfer and overheating.
However, such introduction of steam requires long heating time as often the particles to be heated tend to agglomerate and therefore if such agglomeration occurs the total volume of the agglomerated particles is increased less than the total surface of the agglomerated particles, i.e. the volume to surface ratio is reduced by agglomeration.
Furthermore, the transport of the heat into the particles is governed by the temperature gradient at the surface of the particles and it is therefore an aim to make this gradient as steep as possible.
As mass diffusion in principle is governed by the same measures the above considerations are also relevant for mass diffusion into particles.
Another problem, particularly relevant is that in many of the known processes, shredding/reducing to particles of the raw material is made by a process in which the energy consumed dissipates from the raw material to the surrounding. This is due to the fact that generally shredding/reducing to particles of the raw material is carried out upstream the heating process causing a relevant loss of the processing energy.
U.S. Pat. No. 5,590,961 describes a method of injecting a first fluid into a second fluid to provide a fast temperature increase of the second fluid avoiding destruction of the functional properties of the second fluid.
U.S. Pat. No. 4,303,470 discloses a process and apparatus for mixing chemical with a wood pulp. In one example the chemical is oxygen which is carried to the rotors of a mixer through pipes. In turn radial passages carry the oxygen to the outer manifold and to the pulp through a central passage of the rotor body. The use of the apparatus is limited to mixing chemical and wood pulp as no cutting, milling and grinding elements are present.
That being said, an overall issue to be solved is to reduce a coherent structure of raw-material into separated particles while producing at the same time and intimate contact between the particles and a medium in order to efficiently exchange energy and/or mass.
Often the temperature aimed at is above the boiling temperature of the medium introduced at atmospheric pressure and therefore the pressure needs to be elevated above the atmospheric pressure. Accordingly, an overall issue to be solved is to produce uniform particle size from an inhomogeneous material in an apparatus under pressure while at the same time producing an intimate contact between the produced particles and the medium to allow a chemical reaction, a temperature increase or a combination thereof.
Thus, until now the problem of efficient mixing two media reducing a coherent structure of a first medium into separated particles while producing at the same time and intimate contact between the particles and a second medium in order to efficiently exchange energy and/or mass has not yet been overcome effectively and the present invention seeks at least mitigating some of the problems related thereto.